1. Field of the Invention
Exemplary embodiments of the present invention relate to communication systems; and, more particularly, to an amplifier for amplifying a radio frequency (RF) signal in a communication system, and an apparatus and method for controlling the amplifier.
2. Description of Related Art
Extensive research is being conducted on an amplifier for amplifying signals to a predetermined level in communication systems for stable and normal signal transmission. In particular, with the high integration and miniaturization of semiconductor devices, amplifiers capable of operating stably even in a variable communication environment are being proposed.
In recent communication systems, high-power signals are transmitted in order to stably transmit a large amount of data at a high data rate. Therefore, an amplifier must stably amplify an RF signal and must stably output high-level power. A high power amplifier (HPA) has been proposed as such an amplifier. When an HPA is used to amplify an RF signal in a communication system, the HPA operates at a duty level of 1% to 30%.
A pulse driving scheme is used to drive such an HPA. Examples of the pulse driving scheme include a scheme of switching on/off a drain terminal of the HPA and a scheme of switching on/off a gate terminal of the HPA. A gate bias circuit is used as an HPA driving device.
A communication system uses a plurality of transistor modules for an active phased array, and the miniaturization of the transistor modules is necessary for the miniaturization of the system. That is, for miniaturization of a communication system and miniaturization of a transistor module, an HPA driving device (i.e., a gate bias circuit) must be included in the HPA. If the gate bias circuit is not included in the HPA, it must be included in the transistor module. In this case, the size of the transistor module increases, thus restricting the miniaturization of the system and the miniaturization of the transistor module.
The HPA including the gate bias circuit is driven by switching on/off the drain terminal, because it is not normally driven by switching on/off the gate terminal. That is, in order to drive the HPA including the gate bias circuit, a PWM (Pulse Width Modulation) circuit for switching on/off the drain terminal is included in the transistor module. The size of the transistor module is about 10% of the size of the transistor module, thus restricting the miniaturization of the system and the miniaturization of the transistor module.
In order to overcome the restriction in driving the HPA by the drain terminal on/off scheme, a circuit for turning on/off a gate bias voltage of an FET (Field Effect Transistor) amplifier (i.e., an HPA) and an emitter follower circuit using a BJT (Bipolar Junction Transistor) have been proposed. However, because the circuit for turning on/off a gate bias voltage of an FET amplifier requires additional external devices such as a diode inverter and an operational amplifier, it is difficult to include in the HPA. Also, because the HPA uses an FET device, the emitter follower circuit using a BJT has a limitation on the integration in a single chip. Also, it uses both a positive voltage and a negative voltage to drive the above circuit, thus complicating an external interface.
What is therefore required is an amplifier for stably amplifying an RF signal to a high power in a communication system, and an amplifier controlling scheme that is implemented in the amplifier, thus making it possible to simplify an external interface, reduce the size of a transistor module and reduce the complexity and size of the entire system.